ARM: omap: fix oops in arch/arm/mach-omap2/vp.c when pmic is not found

When the PMIC is not found, voltdm->pmic will be NULL.  vp.c's
initialization function tries to dereferences this, which causes an
oops:

Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = c0004000
[00000000] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT
Modules linked in:
CPU: 0    Not tainted  (3.3.0-rc2+ #204)
PC is at omap_vp_init+0x5c/0x15c
LR is at omap_vp_init+0x58/0x15c
pc : [<c03db880>]    lr : [<c03db87c>]    psr: 60000013
sp : c181ff30  ip : c181ff68  fp : c181ff64
r10: c0407808  r9 : c040786c  r8 : c0407814
r7 : c0026868  r6 : c00264fc  r5 : c040ad6c  r4 : 00000000
r3 : 00000040  r2 : 000032c8  r1 : 0000fa00  r0 : 000032c8
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
Control: 10c5387d  Table: 80004019  DAC: 00000015
Process swapper (pid: 1, stack limit = 0xc181e2e8)
Stack: (0xc181ff30 to 0xc1820000)
ff20:                                     c0381d00 c02e9c6d c0383582 c040786c
ff40: c040ad6c c00264fc c0026868 c0407814 00000000 c03d9de4 c181ff8c c181ff68
ff60: c03db448 c03db830 c02e982c c03fdfb8 c03fe004 c0039988 00000013 00000000
ff80: c181ff9c c181ff90 c03d9df8 c03db390 c181ffdc c181ffa0 c0008798 c03d9df0
ffa0: c181ffc4 c181ffb0 c0055a44 c0187050 c0039988 c03fdfb8 c03fe004 c0039988
ffc0: 00000013 00000000 00000000 00000000 c181fff4 c181ffe0 c03d1284 c0008708
ffe0: 00000000 c03d1208 00000000 c181fff8 c0039988 c03d1214 1077ce40 01f7ee08
Backtrace:
[<c03db824>] (omap_vp_init+0x0/0x15c) from [<c03db448>] (omap_voltage_late_init+0xc4/0xfc)
[<c03db384>] (omap_voltage_late_init+0x0/0xfc) from [<c03d9df8>] (omap2_common_pm_late_init+0x14/0x54)
 r8:00000000 r7:00000013 r6:c0039988 r5:c03fe004 r4:c03fdfb8
[<c03d9de4>] (omap2_common_pm_late_init+0x0/0x54) from [<c0008798>] (do_one_initcall+0x9c/0x164)
[<c00086fc>] (do_one_initcall+0x0/0x164) from [<c03d1284>] (kernel_init+0x7c/0x120)
[<c03d1208>] (kernel_init+0x0/0x120) from [<c0039988>] (do_exit+0x0/0x2cc)
 r5:c03d1208 r4:00000000
Code: e5ca300b e5900034 ebf69027 e5994024 (e5941000)
---[ end trace aed617dddaf32c3d ]---
Kernel panic - not syncing: Attempted to kill init!

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>